Chip resistant primer composition VI

ABSTRACT

A solvent-based thermosetting coating composition comprising a hydroxy functional epoxy resin, linear polycaprolactone diol, and blocked polyisocyanate crosslinking agent. The coating composition may be formulated as hot sprayable, high solids coating composition suitable for use as chip resistant automotive vehicle primer adapted for use on body panel areas subject to chipping by stones, gravel and other road debris. Alternatively, the composition may be formulated as a high solids composition sprayable with conventional spraying equipment. The hydroxy functional epoxy resin is formed by reaction of diepoxide, previously chain extended with diphenol, with hydroxy functional secondary amine in chain terminating reaction.

Reference is made to concurrently filed and commonly assigned relatedU.S. application Ser. Nos. 800,943 entitled "Chip Resistant PrimerComposition VI'" and 800,942 entitled "Chip Resistant Primer CompositionVI"", both to Kordomenos et al.

TECHNICAL FIELD

This invention relates to a solvent-based, thermosetting coatingcomposition comprising hydroxy functional epoxy resins, high molecularweight linear polycaprolactone diol and blocked polyisoycanatecrosslinking agent. It relates also to such coating compositionsformulated, for example, as a hot sprayable, high solids coatingcomposition suitable for use as a chip resistant automotive vehicleprimer adapted for use on body panel areas subject to chipping bystones, gravel and other road debris.

BACKGROUND

Automobile manufacturers, in their efforts to extend the expected lifeof automobile sheet metal and the like, have directed considerableattention to various processes and compositions designed to result innot only improved corrosion resistance but also improved chip resistanceproperties. In particular, research and development efforts haverecently been directed to obtaining primer compositions which areflexible and chip resistant and which give corrosion protection whileexhibiting good humidity and solvent resistance, as well as goodintercoat adhesion. New automobile designs and concern about chipping inareas exposed to stones, gravel and other road debris, e.g. rockerpanels, have demanded such chip resistant primers which can be appliedin reasonable thicknesses by techniques which do not require extensiveand expensive processing modifications during painting operations. Todate available primers, whether high or low solids, have not provensuitable.

In order to overcome the aforementioned chipping problem, it has beencommon to apply relatively thick chip resistant coatings in body panelregions which are inclined to chip, prior to application of stillanother primer composition. One such chip resistant sealer materialwhich has been employed is a polyvinyl chloride plastisol sealer whichhas been applied with airless spraygun equipment in thicknesses of about20 mils in regions subject to high levels of chipping. Problemsattendant with such thick coatings are readily apparent. Because of thethickness in the region to which it is applied, these materials presentan appearance problem often resulting in waviness and roughness in thefinal coating on the sheet metal. Often times surface imperfections alsoresult from the fact that a primer is applied over the top of thissealer, with the primer and sealer being cured together. As a result,some solvent and plasticizer tend to be driven out of the polyvinylchloride plastisol and result in a wavy and rough surface. Still furtherproblems associated with the use of such polyvinyl chloride plastisolsealers and the like involve application technique. Since the polyvinylchloride plastisol sealers and the like must be applied in thicknessesof 20 mils or greater in order to obtain good adhesion, they cannot befeathered down to blend in with other regions of the sheet metal whichdo not require the additional chip protection. Thus, the materials mustbe applied using a masking technique whereby those regions which are notto be coated with the sealer material are masked in a separate operationprior to application of sealer. This masking is then removed after thesealer is applied. It would obviously be desirable to eliminate theseadditional steps in the application of the chip resistant sealermaterial.

Accordingly, it is a preferred object of this invention to provide anovel solvent based, thermosetting coating composition adapted for useas a chip resistant primer, which primer may be applied in thicknessesof less than 20 mils and which may be feathered in such a manner as toblend with paint in other areas of the substrate to be painted which donot require chip resistant coating.

It is another object of the invention to provide novel coatingcompositions which comprise hydroxy functional epoxy resins, highmolecular weight linear polycaprolatone diol and blocked polyisocyanatecrosslinking agent, which provide high crosslinking efficiency andtough, well cured films at minimum bake temperatures such as whenapplied as automotive primers. In this regard, it is a particular objectof the invention to provide a novel thermosetting coating composition ofsufficiently low Volatile Organic Content (VOC) to aid in meetinggovernmental emissions guidelines and yet which can be applied to asubstrate by spraying or other known method.

It is still another object of the invention to provide a compositionwhich will form a coating on a substrate, which coating has advantageousphysical properties including, for example, humidity and solventresistance, flexibility and corrosion protection for the underlyingsubstrate. Additional aspects and advantages of the invention will beapparent from the following description thereof.

DISCLOSURE OF THE INVENTION

According to the present invention, novel thermosetting coatingcompositions are provided which are especially advantageous for use ashigh solids organic solvent based thermosetting coating compositions toprovide chip resistant coatings. The coating composition of thisinvention, in addition to solvent and any pigments and additives suchas, for example, catalysts, and flow control agents and the like,comprises:

(A) hydroxy functional epoxy resin having a number average molecularweight (M ) between about 1,000 and about 4,000 and being the reactionproduct of hydroxy functional secondary amine, in chain terminatingreaction, in approximately 1:1 equivalent ratio with the chain extensionreaction product of diepoxide with diphenol;

(B) linear polycaprolactone diol having a molecular weight of betweenabout 1500 and about 5000, wherein (A) and (B) are included in thecomposition in a weight ratio between about 4:1 and about 1:4; and

(C) blocked polyisocyanate crosslinking agent comprising at least twoisocyanate groups which have been blocked by reaction with an activehydrogen bearing blocking agent which de-blocks at the cure temperatureof the composition, the crosslinking agent being included in thecomposition in an amount equal to between about 10 and about 50 percentof the combined weight of (A) and (B) in the composition.

Particularly preferred compositions of the invention are thoseformulated as high solids coating compositions having solids levels inthe range of 65-80% solids and which are applied as chip resistantprimers in those areas of automotive panels, such as rocker panels,which are exposed to high levels of chipping. Such compositions may beapplied in thicknesses ranging from 1 to 25 mils wet to obtain finalcoatings in the range of 1 to 12 mils dry, and may be feathered down toblend in with paint applied to regions outside that requiring additionalchip resistance protection. Generally, the compositions of this solidslevel may be applied using hot spray equipment at temperatures in therange of about room temperature, i.e., about 70° F., to about 160° F.

Other preferred compositions of the invention are those formulated ashigh solids coating compositions adapted to be applied by conventionalspraying onto a substrate. These high solids coating compositions mayhave a solids level in the range of 50-60% and are especially useful asa primer coating on the bare, unpolished metal surface of an automotivevehicle. As used herein, a high solids coating composition is one havinga volatile organic content of about 479 g/l (4.0 lb./gal.) or less.

Other features and advantages of this invention will become moreapparent from the following, detailed description thereof including thepreferred embodiments and best mode of carrying out this invention.

DETAILED DESCRIPTION OF THE INVENTION

Thermosetting coating compositions of the invention comprise hydroxyfunctional epoxy resin, high molecular weight linear polycaprolactoneand blocked polyisocyanate crosslinking agents. The hydroxy functionalepoxy resin has a number average molecular weight (M ) of between about1,000 and about 4,000 and is the reaction product of diepoxide, whichhas been chain extended with diphenol, with hydroxy functional secondaryamine in chain terminating reaction in approximately 1 to 1 equivalentratio. The linear polycaprolactone diol has a molecular weight ofbetween about 1500 and about 5000, preferably about 2000 and about 4000.These polycaprolactone diols may be prepared by polymerizing lactonemonomers, preferably epsilon-caprolactone monomers, with initiatorscomprising one or more compounds having two functional groups eachhaving an active hydrogen. The hydroxy functional epoxy resin andpolycaprolactone diol are included in the compositions in a weight ratioof between about 1:4 and about 4:1, preferably in a weight ratio ofabout 1:1.

The blocked polyisocyanate crosslinking agent comprises at least twoisocyanate groups which have been blocked by reaction with an activehydrogen bearing blocking agent which de-blocks at cure temperature ofthe composition. The blocked polyisocyanate crosslinking agent isincluded in the composition in an amount equal to between about 10 andabout 50 percent, preferably between about 20 and 40 percent, of thecombined weight of the hydroxy functional epoxy ester resin and linearpolycaprolactone diol in the coating composition. The blockedpolyisocyanate crosslinking agent preferably is selected from the groupconsisting of, but not necessarily limited to, blocked trifunctionalisocyanurate ring containing polyisocyanates and oligoester modifiedblocked isocyanates.

It is believed to be a significant characterizing aspect of the coatingcomposition of the invention that the polycaprolactone portion of thecomposition gives the composition flexibility as well as toughness, twokey properties when choosing a primer for use in areas susceptible tochipping. It is a further characterizing aspect of the composition thatit includes epoxy resin portions, i.e. from the hydroxy functional epoxyresin of the composition, which give the cured compositions excellentcorrosion resistance properties. Still further, it is a characterizingaspect of the invention that the composition contains tertiary aminegroups (i.e., since hydroxy functional secondary amines are used to formthe hydroxy functional epoxy resin, tertiary amine groups are present inthe final resin). Tertiary amine groups are excellent catalysts for theisocyanate crosslinking reaction used to cure compositions of thisinvention.

Preferred hydroxy functional epoxy resins of the invention includesignificant aromatic content which is believed to enhance corrosionresistance properties. Even though aromatics tend to increase thebrittleness of cured compositions including such resins, it is possibleto include them since, as mentioned above, the polycaprolactone portionof the cured composition gives the composition increased flexibilitywhich can more than compensate for any such brittleness. A particularpreferred embodiment of the hydroxy functional epoxy resin of theinvention is prepared from aromatic containing diepoxide which isextended with diphenol. In addition, it is presently understood that thephenolic oxygens introduced into the epoxy resin by the chain extensionreaction of epoxy with phenol advantageously provide excellent adhesionto metal substrates, for example steel.

Each of the above major components of the compositions as well as othercomponents and other aspects of the invention are described hereinafterin greater detail.

A. Hydroxy Functional Epoxy Resin

As described above, this resin is the reaction product of diepoxide,which has been chain extended with diphenol, with hydroxy functionalsecondary amine in chain terminating reaction. Each of the reactantsemployed in the preparation of the hydroxy functional epoxy resin isdescribed in greater detail below.

(i) Diepoxide Reactant

The chain extended diepoxide reactant suitable for preparing the hydroxyfunctional epoxy resin of the composition can be any of numerous chainextended diepoxides including many which are commercially available andwhich will be apparent to the skilled of the art in view of the presentdisclosure. While, ultimately, the choice of diphenol chain extendeddiepoxide reactant for preparing the hydroxy functional epoxy resin willdepend to an extent upon the particular application intended for thecoating composition, terminal diepoxides, that is chain extendeddiepoxides bearing two terminal epoxide groups, are generally mostpreferred. These are generally more reactive and therefore requirereaction conditions under which undesirable side reactions, for example,epoxy-epoxy reactions and gelation, can be more easily avoided.Preferably, the chain extended diepoxide has a number average molecularweight (Mn) between about 1,200 and about 3,500, and more preferablybetween about 1,600 and about 2,400. The diepoxides which are to bechain extended with diphenol be selected from numerous diepoxides, someof which may be diphenol extended diepoxides.

Numerous diepoxides previously extended with diphenol are commerciallyavailable. These include certain of the well known bisphenol-Aepichlorohydrin epoxy resins of the Epon (trademark) series, ShellChemical Company, Houston, Tex., e.g. Epon 1001 and Epon 1004 and theDER (trademark) series, Dow Chemical Company, Midland, Mich., e.g., DER332. These diglycidyl ether bisphenol-A resins or higher molecularweight analogs thereof, are preferred in view of their cost andcommercial availability. Such commercially available diphenol extendeddiepoxides may be used as is or may be further extended by diphenol inorder to give higher molecular weight materials having desirableproperties.

Other suitable diepoxy resins, not previously extended with diphenol,may be extended with diphenol and used in the preparation of the hydroxyfunctional epoxy resin. Preferred diepoxy resins of this type includeEpon 828 (trademark) and Epon 829 (trademark) which are nonextendeddiepoxides of the aforementioned Epon Series, as well as cycloaliphaticdiepoxy resins such as the Eponex (trademark) series, Shell ChemicalCompany, hydantoin epoxy resins such as, for example, Resin XB2793(trademark), Ciba-Geigy Corporation, Ardsley, N.Y.; and any of a widevariety of acyclic or cyclic aliphatic diepoxides such as, for example,1,4-butanediol diglycidyl ether and 4-vinylcyclohexene dioxide and thelike. Other suitable diepoxides, either previously extended withdiphenol or not so extended, are available and will be apparent to theskilled of the art in view of the present disclosure. Also, it will beunderstood from the foregoing that any mixture of compatible extendeddiepoxides may be used.

In addition to the diphenol chain extended diepoxide, a portion of theepoxide functionality can be provided by any compatible monoepoxycompound or polyepoxy compound which also may be diphenol chain extendedor a mixture of such compounds. The polyepoxide can be any of the wellknown types such as polyglycidyl ethers of polyphenols. These can beproduced by etherification of polyphenol with epihalohydrin in thepresence of alkali. It will be recognized by the skilled of the art inview of the present disclosure, that in some instances, particularlywhere a coating composition of high solids content is less important, itmay be desirable to incorporate polyepoxide of higher molecular weight.Preferably, any such polyepoxide contains free hydroxyl groups inaddition to epoxide groups. While polyglycidyl ethers of polyphenol canbe employed, it may be desirable to react a portion of the reactivesites (hydroxyl or in some instances epoxy) with a modifying material tovary the film characteristics of the epoxy resin. The epoxy resin may bemodified, for example, with isocyanate group containing organicmaterials or other reactive organic materials. Other useful polyepoxidesare the novolak resins including, for example, the novolak epoxy resinsECN 1235 (trademark) and ECN 1273 (trademark), Ciba-Geigy Corporation.According to preferred embodiments of the present invention, epoxidecompounds other than diepoxide compounds provide no more than about 15%and most preferably substantially none of the total epoxidefunctionality in the reactants used to form the epoxy resin.

(ii) Diphenol Reactant

The diphenol reactants suitable for reaction with a diepoxide reactantin chain extension reaction, in those instances where initial or furtherextension with diphenol are required, include numerous commerciallyavailable materials, many of which will be readily apparent to theskilled of the art in view of the present disclosure. Preferreddiphenols have the general formula (I): ##STR1## wherein R is a divalentlinking moiety substantially unreactive with the diepoxide resin.Preferably R is a divalent organic linking moiety, for example (CH₂)_(n)where n is preferably from about 1 to about 8, C═O, and the like,although inorganic moieties, for example sulfonyl and the like, are alsosuitable. Diphenols of this character have been found to provide goodreactivity with diepoxides described above and to provide, ultimately,cured coatings of the invention having excellent physical properties,most notably excellent corrosion protection. It will be apparent to theskilled of the art in view of the present disclosure that R should besubstantially unreactive with the hydroxy functional secondary amineemployed in preparation of the hydroxy functional epoxy resin.Particularly preferred diphenols include those according to formula (I)above, wherein R is selected from the group comprising a straight orbranched alkylene or alkylidene moiety of one to about 10 carbons,preferably having three to four carbons and most preferably having thegeneral formula: ##STR2## wherein R' and R" are the same or differentand each is a monovalent organic moiety preferrably selected from thegroup comprising hydrogen and lower alkyl of about one to four carbons,most prefereably one or two carbons, and the like or a mixture of any ofthem. Preferably the diphenol has a number average molecular weight (Mn)between about 180 and about 500, more preferably between about 180 andabout 250. Such diphenols include, for example bisphenol-A, which ismost preferred, bisphenol-B, bisphenol-F and the like and a compatiblemixture of any of them. As used herein the term diphenol may include,for example, compounds comprising a single dihydroxy substituted phenylring such as benzenediol. More preferred, however, are those diphenolsproviding two terminal, monohydroxy substituted phenyl rings such as informula (I), above. Other examples of diphenols arebis-(4-hydroxy-tertbutylphenyl)-2,2-propane,bis-(2-hydroxy-naphthyl)-methane and 1,5-dihydroxynaphthalene. Othersuitable diphenols for preparation of the hydroxy functional epoxy resinof the present invention will be apparent to the skilled of the art inview of the present disclosure.

(iii) Hydroxy Functional Secondary Amine Reactant

The hydroxy functional secondary amine which is reacted in chainterminating reaction with the reaction product of the above describeddiepoxide and diphenol may be selected from a broad class of aliphatic,cycloaliphatic and aromatic hydroxy functonal amines.

Numerous such amines, which may bear mono- or dihydroxy functionalitywill be apparent to those skilled in the art in view of the presentdisclosure. Exemplary of such amines are those having the formula (II):##STR3## wherein R and R' are selected from the group consisting ofaliphatic, cycloaliphatic and aromatic radicals which will not interferewith the chain termination reaction between the chain extended diepoxideand the hydroxy functional secondary amine. R and R' in the aboveformula may be the same or different, but preferably should be of thesame nature. X may be selected from hydrogen and hydroxyl radical.

While the hydroxyl group on R and/or R' may be other than primary,primary hydroxyls are preferred since such primary hydroxyl groups aremore reactive (i.e., they react faster) with the polyisocyanatecrosslinking agent of the composition during curing.

Examples of preferred radicals R and R' for the hydroxy functional amineof the above formula (II) are:

    ______________________________________                                        (CH.sub.2).sub.n      where n = 1-5;                                          (CH.sub.2 CH.sub.2 O).sub.n CH.sub.2 CH.sub.2                                                       where n = 1-12;                                          ##STR4##             where n = 1-12; and                                      ##STR5##             where n = 1-12.                                         ______________________________________                                    

Preferably R and R' are methylene, ethylene, or lower alkylene groupsbut they may be any other noninterfering radical including those, forexample, such as benzyl, oxyalkylene, etc.

Particularly preferred primary hydroxyl bearing amines for use inpreparing the hydroxy functional epoxy resin are diethanol amine,methylethanol amine, dipropanol amine, and methylpropanol amine.

The hydroxy functional epoxy resin of the invention can be madeaccording to techniques well known to the skilled of the art. The chainextension, where necessary, and chain termination reactions occursequentially, with the chain extension of the diepoxide being carriedout first. Diepoxide and diphenol are charged into a suitable reactorand heated. The reactants are used in relative proportions to yield achain extension reaction product bearing two unreacted epoxy groups andpreferably substantially no unreacted phenol functionality. Suitableseparation techniques are known to the skilled of the art for removal ofunused reactants. It should be recognized that to assure rapid and/ormore complete reaction of the diepoxide with the phenol functionality,it is usually preferred to have a catalyst present. The use of catalysthas been found to provide advantageous hydroxy functional epoxy resin ofthe invention and is preferred. Epon 829 (trademark), mentioned above,as sold, provides a proprietary catalyst. Epon 828 (trademark), issubstantially the same but does not provide such catalyst. Suitablecatalysts are commerically available and include any of the well knowncatalysts for epoxy-phenol reactions such as sodium carbonate, lithiumneodecanoate and other organo metalic catalysts and tertiary amines,such as borzyl dimethylamine, which is preferred. Still other preferredcatalysts include formylmethylene triphenylphorane,formylmethyltriphenylphosphonium chloride, methyltriphenylphosphoniumiodide, ethyltriphenylphosphonium acetate. Other suitable catalysts willbe apparent to those skilled in the art in view of the presentdisclosure.

The reaction mixture is heated to at least about 35° C. (280° F.). Whenin the presence of catalysts, exothermic reaction will proceed with orwithout further heating. Typically, the reaction mixture will then readabout 170° C.-190° C. (340° F.-370° F.), depending upon the batch sizeand reactor vessel insulation, etc. In the absence of catalyst, suchexotherm is typically not observed and continued heating is required.The progress of the reaction can be followed by measuring weight perepoxide (WPE), that is, epoxy equivalent weight.

After completion of the chain extension reaction, the hydroxy functionalsecondary amine reactant is charged into the reaction vessel. Thisreaction is exothermic and drives itself to completion. As noted above,the chain extended reaction product is reacted with hydroxy functionalsecondary amine in chain terminating reaction in approximately 1 to 1equivalent ratio, i.e., approximately 1 to 1 equivalent ratio of epoxidegroups to amine groups. This ratio is desirable since excess epoxy couldresult in gelation of the reaction mixture, while excess amine remainingin the reaction mixture could react with some of the polyisocyanatecrosslinking agent in the composition, which would then not be availablefor curing the coating compositions resins. For this reason, if excessamine is used during formation of the hydroxy functional resin; itshould preferably be removed prior to combination of the hydroxyfunctional epoxy resin with the polycaprolactone diol and blockedpolyisocyanate crosslinking agent.

B. Linear Polycaprolactone Diol

The linear polycaprolactone diol employed in the coating composition ofthe present invention has a molecular weight of between about 1500 andabout 5000, preferably between about 2000 and about 4000. Numeroussuitable polycaprolactone diols will be apparent to the skilled of theart in view of the present disclosure and include, for example, thoseformed by polymerizing lactones in the presence of an initiator bymethods well known to those skilled in the art. Suitable linearpolycaprolactone diols also are commercially available, for example,from Union Carbide, Danbury, Conn. in the TONE (trademark) Series, e.g.,TONE 0260. This series comprises polycaprolactone diols as well aspolycaprolactone triols.

The preparation of suitable linear polycaprolactone diols is described,for example, in U.S. Pat. Nos. 2,914,556 and 3,169,945 to Hostettler etal. Polymerization of the lactone monomer to form the polycaprolatonediol of this invention is initiated by reaction with one or morecompounds having two functional groups each having an active hydrogencapable, with or without the aid of a catalyst, of opening the lactonering and adding it as an open chain without forming water ofcondensation. Compounds suitable for use to initiate the polymerizationof the lactones, referred to herein as initiators, include, but are notlimited to, diamines, diols, amino alcohols, diacids, andhydroxy-carboxylic acids. Also suitable are amides, sulfonamides,hydrozones, carbazone and oximes containing two reactive groups. Thelactone starting material which may be employed in forming thepolycaprolactone diol component of the invention may be any lactone, orcombination of lactones, having at least six carbon atoms, for example,from six to eight carbon atoms, in the ring and at least one hydrogensubstituent on the carbon atom which is attached to the oxy group insaid ring. In one aspect, the lactone used as a starting material can berepresented by the general formula: ##STR6## in which n is at leastfour, for example, from four to six, at least n+2R's are hydrogen, andthe remaining R's are substituents selected from the group consisting ofhydrogen, alkyl, cycloalkyl, alkoxy and single ring aromatic hydrocarbonradicals. Lactones having greater numbers of substituents other thanhydrogen on the ring, and lactones having five or less carbon atoms inthe ring, are considered unsuitable for the purposes of the inventionbecause of the tendency that polymers thereof have to revert to themonomer, particularly at elevated temperature.

The lactones preferred in this invention for forming thepolycaprolactone diol are the epsilon-caprolactones having the generalformula: ##STR7## wherein at least six of the R's are hydrogen and theremainder are hydrogen, alkyl, cycloalkyl, alkoxy or single ringaromatic hydrocarbon radicals, none of the substituents contain morethan about twelve carbon atoms, and the total number of carbon atoms inthe substituents on a lactone ring does not exceed about twelve.Unsubstituted epsilon-caprolactone, in which all the R's are hydrogen,is derived from 6-hydroxyhexanoic acid and is most preferred.Substituted epsilon-caprolactones, and mixtures thereof, are availableby reacting a corresponding substituted cyclohexanone with an oxidizingagent such as peracetic acid.

Among the substituted epsilon-caprolactones considered most suitable forthe purposes of the invention are the various monoalkylepsilon-caprolactones such as the monomethyl-, monoethyl-, monopropyl-,monoisopropyl-, etc. to monododecyl epsilon-caprolactones; dialkylepsilon-caprolactones in which the two alkyl groups are substituted onthe same or different carbon atoms, but not both on the epsilon carbonatom; trialkyl epsilon-caprolactones in which two or three carbon atomsin the lactone ring are substituted, so long as the epsilon carbon atomis not disubstituted; alkoxy epsilon-caprolactones such as methoxy andethoxy epsilon-caprolactones; and cycloalkyl, aryl, and aralkylepsilon-caprolactones such as cyclohexyl, phenyl and benzylepsilon-caprolactones.

Lactones having more than six carbon atoms in the ring, e.g.,zeta-enatholactone and eta-caprylolactone may also be polymerized toform the linear polycaprolactone diol employed in the invention.

Diols that are suitable as bifunctional initiators include glycols ofthe formula HO(CH₂)_(n) OH in which n equals 2 to 10, glycols of theformula HO(CH₂ CH₂ 0)_(n) H and HO(CHCH₃ CH₂ 0)_(n) H in which n equals1 to 40, such as ethylene glycol, diethylene glycol, and the like,2,2-dimethyl- 1,3-propanediol, 2,2-diethyl-1,3-propanediol,3-methyl-1,5-pentanediol, N-methyl- and N-ethyl- diethanol amines,various cyclohexanediols such as 4,4'-methylenebiscyclohexanol,4,4'-isopropyl-idenebiscyclohexanol, various xylenediols, varioushydroxymethyl-phenethyl alcohols, various hydroxymethyl-phenylpropanols,various phenylenediethanols, various phenyldipropanols, and variousheterocyclic diols such as 1,4-piperazinediethanol. Other suitable diolsinclude polyoxyalkylated derivatives of difunctional compounds havingtwo reactive hydrogen atoms. These difunctional compounds may containprimary or secondary hydroxyls, phenolic hydroxyls, primary or secondaryamino groups, amido, hydrazino, guanido, ureido, mercapto, sulfino,sulfonamide, or carboxyl groups. They are obtainable by reacting diolsof the class HO(CH₂)_(n) OH, wherein n equals 2 to 10, propylene glycol,thiodiethanol, xylenediols, 4,4'-methylenediphenol,4,4'-isopropylidene-diphenol, and resorcinol; mercapto alcohols, likemercaptoethanol; dibasic acids, such as maleic, succinic, glutaric,adipic, pimelic, sebacic, phthalic, tetrahydrophthalic, andhexahydrophthalic; phosphorous acid; aliphatic, aromatic andcycloaliphatic primary monoamines, like methylamine, ethylamine,propylamine, butylamine, aniline, cyclohexylamine; secondary diamines,like N,N'-dimethylethylenediamine; and amino alcohols containing asecondary amino group, like N-methylethanolamine, with alkylene oxidessuch as ethylene oxide, propylene oxide, 1-butylene oxide, 2-butyleneoxide, isobutylene oxide, butadiene monooxide, styrene oxide, and alsomixtures of these monoepoxides.

Other useful bifunctional initiators are polymers of monoepoxidesobtainable by polymerizing with such catalyst as oxonium salts ofhydrogen halides; metal or nonmetal halides whose etherates are oxoniumcomplexes; electrophilic metal or non-metal halides in the presence ofhydrogen halides, acyl halides, or anhydrides of inorganic and organicacids; and inorganic acids or anhydrides thereof whose anions showlittle tendency to polarize. Polymers containing hydroxyl end groups canbe obtained by treating these products with alkaline reagents uponcompletion of the polymerization reaction. Among suitable monoepoxidesfor preparing such polymers are tetrahydrofuran, trimethylene oxide,propylene oxide, ethylene oxide and mixtures thereof.

Difunctional amino alcohols capable of initiating the polymerization oflactones include aliphatic amino alcohols of the general formulaHO(CH₂)_(n) NH₂, wherein n equals 2 to 10, N-methylethanolamine,isopropanolamine N-methylisopropanolamine, aromatic amino alcohols likepara-amino-phenethyl alcohol, and para-amino-alphamethylbenzyl alcohol,and various cycloaliphatic amino alcohols like 4-amino-cyclohexanol.

Suitable diamines include aliphatic diamines of the general formula H₂N(CH₂)_(n) NH₂ ; monosecondary diamines of the general formulaR"NH(CH₂)_(n) NH₂ ; disecondary diamines of the general formulaR"NH(CH₂)_(n) NHR", where n equals 2 to 10 and where R" is alkyl, aryl,aralkyl or cycloalkyl; aromatic diamines, like metaphenylenediamine,para-phenylenediamine, toluene-2,4-diamine, toluene-2,6-diamine,1,5-naphthalenediamine, 1,8-naphthalenediamine, meta-xylylenediamine,para-xylylenediamine, benzidine, 3,3'-dimethyl-4,4'-biphenyldiamine,3,3'-dimethoxy-4,4'-bi-phenyldiamine,3,3'-dichloro-4,4'-biphenyldiamine, 4,4'-methyleneo dianiline,4,4'-ethylenedianiline, 2,3,5,6,-tetramethylpara-phenylenediamine,2,5-fluorenediamine, and 2,7-fluorenediamine; cycloaliphatic diamineslike 1,4-cyclohexanediamine, 4,4'-methylenebiscyclohexylamine, and4,4'-isopropylidenebiscyclohexylamine; and heterocyclic amines such aspiperazine, 2,5-dimethylpiperazine, and1,4-bis(3-aminopropyl)piperazine.

Representatives of the many dicarboxylic acids that are suitable asbifunctional initiators are such dicarboxylic acids as oxalic acid,succinic acid, maleic acid, glutaric acid, adipic acid, pimelic acid,suberic acid, azelaic acid, sebacic acid, 4,4'-oxydibutyric acid,5,5'-oxydivaleric acid, 6,6'-oxydihexanoic acid, 4,4'-thiodibutyricacid, 5,5'-thiodivaleric acid, 6,6'-thiodihexanoic acid, itaconic acid,phthalic acid, isophthalic acid, terephthalic acid, 1,5-naphthoic acid,2,7-naphthoic acid, 2,6-naphthoic acid, 3,3'-methylenedibenzoic acid,various tetrahydrophthalic acids, and various hexahydrophthalic acids.

Suitable hydroxy- and aminocarboxylic acids include 2-hydroxypropionicacid, 6-hydroxycaproic acid, 11-hydroxy-undecanoic acid, salicylic acid,parahydroxybenzoic acid, beta-alanine, 6-aminocaproic acid,7-aminoheptanoic acid, 11-amino-undecanoic acid, and paraaminobenzoicacid.

The initiator is believed to open the lactone ring to produce an esteror amide having two terminal groups that are capable of opening furtherlactone rings and thereby of adding more and more lactone to themolecule. Thus, for example, the polymerization of epsilon-caprolactoneinitiated with a diol is believed to take place primarily as follows:##STR8## wherein a is the total number of mols of lactone reacted permol of initiator and b+c=a.

To initiate and continue the polymerization of the lactone, the lactoneand the initiator are preferably heated to a temperature between about130° and 200° C. In order to achieve a practical and desirable rate ofreaction with a minimum of decomposition. The temperature may beconsiderably lower however, i.e., as low as about 50° C. at thesacrifice of speed of reaction. It may also be considerably higher,i.e., up to about 300° C., although care must be taken at such highertemperatures because of the more likely losses, at temperatures above250° C., due to decomposition or undesirable side reactions. Generally,therefore, a temperature range of 50° to 300° C. is considered operableand a more limited range between about 130° and 200° C. is consideredpreferable.

It is within the ability of the skilled in the art to determine asuitable amount of initiator to use to achieve a linear polycaprolactonediol of desired molecular weight. The polymerization may be, andpreferably is, carried out with the use of a catalyst, such as a basicor neutral ester interchange catalyst, to accelerate the reaction. Amongcatalysts suitable for this purpose are such metals as lithium, sodium,potassium, rubidium, cesium, magnesium, calcium, barium, strontium,zinc, aluminum, titanium, cobalt, germanium, tin, lead, antimony,arsenic and cerium, as well as the alkoxides thereof. Additionalsuitable catalysts are, by way of example, the carbonates of alkali- andalkaline earth metals, zinc borate, lead borate, zinc oxide, leadsilicate, lead arsenate, litharge, lead carbonate, antimony trioxide,germanium dioxide, cerium trioxide, cobaltous acetate and aluminumisopropoxide. Catalyst concentrations between about 0.001 and 0.5%,based on the weight of the starting lactones, are suitable. Thepreferred range is from 0.01 to 0.2%.

While not wishing to be bound by theory, it is presently understood thatthe linear polycaprolactone diol is characterized by the presence ofseries of interconnected, substantially linear units or groups composedof carbon, hydrogen and oxygen. The interconnected units are openedlactone residues each having a terminal oxy group at one end, a carbonylgroup at the other end, an intermediate chain of at least five carbonatoms and at least one hydrogen substituent on the carbon atom in theintermediate chain that is attached to the terminal oxy group. The oxygroup of one lactone residue is connected to the carbonyl group of anadjacent lactone residue in the series and the oxy group of the lastlactone residue in a series is connected to a hydrogen to form aterminal hydroxyl group at the end of the series.

The hydroxy functional epoxy resin and the linear polycaprolactone diolare included in the coating composition in a weight ratio of betweenabout 1:4 and 4:1, preferably in a weight ratio of about 1:1.

C. Blocked Polyisocyanate Crosslinking Agent

The crosslinking agent employed in the novel solvent based coatingcompositions of the invention comprises blocked polyisocyanate. Thenovel solvent based coating compositions of the invention, as a resultof employing blocked polyisocyanate crosslinking agents, exhibitexceptional shelf stability even when corrosion inhibiting pigments suchas zinc chromate are used in high concentrations.

As used herein "blocked polyisocyanate" means an isocyanate compoundcontaining two or more isocyanate groups, all of which have been reactedwith a material which will prevent reaction of the isocyanate group atroom temperature with compounds that conventionally react with suchgroups, and at least some of which will permit that reaction to occur athigher (cure) temperatures. In general the blocked polyisocyanate may beprepared by reacting a sufficient quantity of an active hydrogencontaining blocking agent with the polyisocyanate to insure that no freeisocyanate groups are present. The blocking agent may be represented bythe formula BH and may be selected from numerous materials, hereinafterdiscussed, which bear an active hydrogen.

The blocked polyisocyanate crosslinking agent is included incompositions of the invention in an amount equal to between about 10 and50 percent, preferably in an amount equal to between about 20 and 40percent, of the combined weight of hydroxy functional epoxy resin (A)and linear polycaprolactone diol (B) in the coating composition. Thecrosslinking agent deblocks at the cure temperature of the coatingcomposition.

Blocked polyisocyanates of numerous types may be employed in thecompositions of the invention. Particularly suitable blockedpolyisocyanates, which will be discussed further hereinafter, includeblocked polymethylene polyphenol isocyanates, isocyanurate ringcontaining blocked polyisocyanates and certain oligoester modifiedblocked polyisocyanates

In the preparation of the blocked polyisocyanate crosslinking agent, anysuitable organic polyisocyanate may be used. Representative examples arethe aliphatic compounds such as trimethylene, tetramethylene,pentamethylene, hexamethylene, 1,2-propylene, 1,2-butylene,2,3-butylene, 1,3-butylene, ethylidine and butylidene diisocyanates; thecycloalkylene compounds such as 1,3-cyclopentane, 1,4-cyclohexane, and1,2-cyclohexane diisocyanates; the aromatic compounds such asm-phenylene, p-phenylene, 4,4'-diphenyl, 1,5-naphthalene, and1,4-naphthalene diisocyanates, the aliphatic-aromatic compounds such as4,4'-diphenylene methane, 2,4- or 2,6-tolylene, or mixtures thereof,4,4'-toluidine, and 1,4-xylylene diisocyanates; substituted aromaticcompounds such as dianisidine diisocyanate, 4,4'-diphenyletherdiisocyanate and chlorodiphenylene diisocyanate; the triisocyanates suchas triphenyl methane-4,4'4"- triisocyanate, 1,3,5-triisocyanate benzeneand 2,4,6-triisocyanate toluene; the tetraisocyanates such as4,4'-diphenyl-dimethyl methane-2,2',5,5'-tetraisocyanate; and thepolymerized polyisocyanates such as tolylene diisocyanate dimers andtrimers, and the like.

In addition, the organic polyisocyanate may be a prepolymer derived froma polyol including polyether polyol or polyester polyol, includingpolyethers which are reacted with excess polyisocyanates to formisocyanate-terminated prepolymers. The polyols may be simple polyolssuch as glycols, e.g., ethylene glycol and propylene glycol, as well asother polyols such as glycerol; trimethylolpropane, pentaerythritol, andthe like, as well as mono-ethers such as diethylene glycol, tripropyleneglycol and the like and polyethers, i.e., alkylene oxide condensates ofthe above. Among the alkylene oxides that may be condensed with thesepolyols to form polyethers are ethylene oxide, propylene oxide, butyleneoxide, styrene oxide and the like. These are generally calledhydroxyl-terminated polyethers and can be linear or branched. Examplesof polyethers include polyoxyethylene glycol, polyoxypropylene glycol,polyoxytetramethylene glycol, polyoxyhexamethylene glycol,polyoxynonamethylene glycol, polyoxydecamethylene glycol,polyoxydodecamethylene glycol and mixtures thereof. Other types ofpolyoxyalkylene glycol ethers can be used. Especially useful polyetherpolyols are those derived from reacting polyols such as ethylene glycol,diethylene glycol, triethylene glycol, 1,4-butylene glycol, 1,3-butyleneglycol, 1,6-hexanediol, and their mixtures; glycerol, trimethylolethane,trimethylolpropane, 1,2,6-hexanetriol, pentaerythritol,dipentaerythritol, tripentaerythritol, polypentaerythritol, sorbitol,methyl glucosides, sucrose and the like with alkylene oxides such asethylene oxide, propylene oxide, their mixtures, and the like.

A particular class of aromatic polyisocyanates which may be employed inthe novel solvent based coating compositions of the invention arepolymethylene polyphenol isocyanates having the formula: ##STR9##wherein n equals 1 to 3. Such compounds, sold under the tradename "PAPI"by the UpJohn Chemical Company of Kalamazoo, Mich., have proven to beparticularly useful in compositions of the invention, resulting incompositions exhibiting desirable toughness in the final cured coating.

The active hydrogen containing blocking agents which are reacted withthe above described organic diisocyanates may be selected from numerousblocking agents which will be apparent to those skilled in this art.Representative of those blocking agents which are preferred are thoseselected from the group consisting of (i) aliphatic, cycloaliphatic andaromatic alkyl monoalcohols; (ii) hydroxyl amines; (iii) oximes; (iv)lactams; and (v) triazoles. Any suitable aliphatic, cycloaliphatic oraromatic alkyl monoalcohol may be used as a blocking agent in accordancewith the present invention. For example, aliphatic alcohols, such asmethyl, ethyl, chloroethyl, propyl, butyl, amyl, hexyl, heptyl, octyl,nonyl, 3,3,5-trimethylhexyl, decyl, and lauryl alcohols, and the likemay be employed. Suitable cycloaliphatic alcohols include, for example,cyclopentanol, cyclohexanol and the like, while aromatic-alkyl alcoholsinclude phenylcarbinol, methylphenylcarbinol, and the like. Minoramounts of even higher molecular weight relatively non-volatilemonoalcohols may be used, if desired, to serve as plasticizers in thecoatings provided by the invention. Examples of hydroxyl amines whichmay be employed as blocking agents include ethanol amine and propanolamine. Suitable oxime blocking agents include, for example,methylethylketone oxime, acetone oxime and cyclohexanone oxime. Examplesof lactams which may be used as blocking agents are epsilon-caprolactam,epsilon-butyrolactam and pyrrolidone, while suitable triazoles includecompounds such as 1,2,4-triazole, 1,2,3-benzotriazole, 1,2,3-tolyltriazole and 4,5-diphenyl-1,2,3-triazole. Particularly preferred activehydrogen containing blocking agents are methylethyl ketoxime and2-ethylhexanol.

(i) Isocyanurate Ring Containing Blocked Isocyanate Compounds

Within the scope of the above general class of blocked polyisocyanatecrosslinking agents, a particular class type of blocked polyisocyanatecrosslinking agent which may be employed in the novel solvent basedcoating compositions of the invention comprises isoycanurate ringcontaining blocked isocyanate compounds. In general, these blockedpolyisocyanates may be formed by blocking with the aforementionedblocking agent isocyanurate ring containing polyisocyanates. Thesecompounds may be formed by cyclotrimerization of difunctionalisocyanates. Usually, the reaction does not stop in this stage andcontinues through the formation of polyfunctional oligomers or a mixtureof such oligomers with a portion of the pure trifunctionalpolyisocyanate. Mixtures of trifunctional product and variouspolyfunctional oligomers are commercially available.

A particularly desirable blocked polyisocyanate crosslinking agent isthe blocked form of the pure trifunctional isocyanurate represented bythe following formula: ##STR10## wherein R is selected from the groupconsisting of aliphatic, cycloaliphatic and aromatic groups andcombinations thereof and B is the residue of an active hydrogencontaining blocking agent. More specifically, this compound is disclosedin U.S. Pat. No. 4,491,663, the disclosure of which is herebyincorporated by reference.

(ii) Oligoester Modified Blocked Polyisocyanates

Still further particular blocked polyisocyanates useful as crosslinkingagents in the novel solvent based coating compositions of this inventionare oligoester modified blocked polyisocyanates prepared from aparticular class of oligoester diols and triols. A first type of sucholigoester modified blocked polyisocyanates is prepared from organicdiisocyanates bearing one isocyanate group more reactive than the other,with the more reactive isocyanate first being blocked with a blockingagent and the remaining isocyanate group then being reacted withhydroxyl functionality of an oligoester diol or triol as referred toabove. The second type of oligoester modified blocked polyisocyanate maybe prepared by reacting oligoester diols from the aforementioned classof oligoesters with an excess of organic diisocyanate so as to form anisocyanate terminated prepolymer followed by blocking of the terminalisocyanate groups of the prepolymer with an active hydrogen containingblocking agent. Each of these materials is particularly useful in thecompositions of the invention and produces final cured coatingcompositions exhibiting outstanding flexibility.

Oligoesters of the type employed in the preparation of thesecrosslinking agents are described in U.S. Pat. No. 4,322,508 issued Mar.30, 1982, the disclosure of which is hereby incorporated by reference.The hydroxy functional oligoesters within the useful class of materials(i) have a number average molecular weight (Mn) between about 150 andabout 3000, preferably between about 230 and about 1000, (ii) bear 2 or3 hydroxyl groups per molecule, and (iii) are formed by anesterification reaction between a carboxylic acid and an epoxide. Theesterification reaction products are selected from the group consistingof:

(a) the esterification reaction product of polycarboxylic acid, i.e.,carboxylic acid bearing 2 or more carboxyl groups, and monoepoxide;

(b) the esterification reaction product of polyepoxide, i.e., a compoundhaving 2 or more epoxide groups, and monocarboxylic acid, preferablycontaining no ethylenic unsaturation, and bearing no hydroxyfunctionality;

(c) the esterification reaction product of hydroxy functional carboxylicacid and mono- or polyepoxide, preferably monoepoxide;

(d) the esterification reaction product of monocarboxylic acid andhydroxy functional mono

polyepoxide, preferably monoepoxide; and

(e) mixtures of (a)-(d).

As noted above, the first type of oligoester modified blockedpolyisocyanate crosslinking agent is prepared by (i) reacting organicdiisocyanate bearing one isocyanate group which is more reactive thanthe other with a sufficient amount of an active hydrogen containingblocking agent to react substantially with all of the more reactiveisocyanate groups, thus providing a half-blocked diisocyanate and (ii)reacting this half-blocked intermediate with the above discussedoligoester. The organic diisocyanates employed in this synthesis, aswell as the active hydrogen containing blocking agents, are discussedabove in connection with the preparation of the isocyanurate ringcontaining blocked isocyanate crosslinking agents useful in compositionsof the invention. The organic polyisocyanate-blocking agent adductintermediate is formed by reacting a sufficient quantity of the blockingagent with the organic diisocyanate to insure that one of the two -NCOgroups on the diisocyanate is reacted. The reaction between the organicdiisocyanate and the blocking agent is exothermic; therefore, thediisocyanate and the blocking agent are preferably admixed attemperatures no higher than about 80° C., preferably below about 50° C.,to minimize the exothermic effect.

This intermediate is next reacted with the oligoester diol or trioldescribed above so as to react substantially all free or unblockedisocyanato groups of the diisocyanate/blocking agent intermediate withhydroxyl groups of the oligoester. This reaction is carried outdesirably at a temperature of about 80°-120° C.

As also discussed above, the second type of oligoester modified blockedpolyisocyanate crosslinking agent useful in the novel solvent basedcoating compositions of the invention is prepared by reacting an excessof organic diisocyanate with an oligoester diol from the above describedclass of oligoesters followed by reaction of the terminal isocyanategroups formed on the resulant prepolymer with an active hydrogencontaining blocking agent as described above so as to react withsubstantially all the isocyanate groups. The diisocyanate startingmaterial is used in excess in amounts sufficient to insure that theintermediate is isocyanate terminated. Therefore, it is preferable thatthe organic diisocyanates and the dihydroxy functional oligoester bereacted in a molar ratio of from greater than 1:1 up to 2:1. Numerousdiisocyanates of the type described hereinbefore may be employed in thepreparation of this intermediate. While it is not necessary that oneisocyanate group be more reactive than the other, the preparation ofthis type of crosslinking agent does not preclude the use of suchmaterial.

D. General Discussion--Other Aspects of Invention and Other Components

The coating compositions of the invention have been found to provide acured coating having the advantageous physical properties describedabove, over a wide range of cure temperatures and a wide range of solidslevels. More specifically, the coating compositions according topreferred embodiments of the invention have been found to cure attemperatures from as low as about 120° C. or less within about 15minutes or less, and yet to cure and suffer no significant loss ofadvantageous physical properties at temperatures as high as about 200°C. or more for periods up to about 60 minutes or more. Consideredtogether with the storage stability of the coating composition, it canbe readily recognized that the present invention provides a highlysignificant advance in the coating composition art.

It will be within the skill of the art to determine the proper volatileorganic content for a given coating composition of the invention and fora given application. Preferred solvents have relatively low volatilityat temperatures appreciably below their boiling points such that solventevaporation is low during storage and/or application of the coatingcomposition to the substrate. A suitable solvent system may include, forexample, toluene, methyl ethyl ketone, isobutyl acetate, xylene,cellosolve acetate, acetone and a mixture of any of them. Other solventswhich may be employed include terpenes, aliphatic and aromatic naphthas,and the like. Additional suitable solvents are commercially availableand will be apparent to the skilled of the art in view of the presentdisclosure.

Any solvent allowed to remain in the cured coating should be inert so asto avoid adverse effect upon the cured coating or upon another coatinglayer used in conjunction with it during the curing process orthereafter. Preferrably, the cured coating is substantially free ofsolvent.

Sufficient solvent is used to reduce the viscosity of the coatingcomposition to a level suitable for application to the substrate in thedesired manner.

Obviously, in those cases where the composition is to be applied as achip resistant primer the amount of solvent will be reduced so as togive a solids level of about 65-80%. Such higher solids materials aregenerally applied using hot spray equipment.

Flow control agent(s), for example, polybutyl acrylate; wettingagent(s), for example, silicone; pigments; pigment dispersants;corrosion inhibitors, for example, chromate pigments, numerous of all ofwhich are known to the skilled of the art, may be employed in thecoating compositions of the invention. In addition, suitable reactiveadditives can be used, including, for example, low molecular weight diolflow control agents and reactive diluents.

Compositions of the invention, and in particular the chip resistantprimers of the invention, may also include anti-settling or anti-saggingagents to control the thixotropic properties of the composition.Exemplary of available materials suitable for this purpose are Dislon(trademark) 6900-20X manufactured by Kusumoto Chemicals, Ltd., Tokyo,Japan and sold by King Industries, Norwalk, Conn. 06852; Bentone(trademark) 38, N. L. Industries, Highstown, N.J. 08520; and Cab-O-Sil(trademark) M-5, Cabot Corporation, Boston, Mass.

Curing the coating composition requires baking for sufficient time atsufficiently elevated temperature to react the crosslinking agent withthe hydroxyl functionality of the hydroxy functional epoxy resin andlinear polycaprolactone diol. The time and temperature required to curethe coating are interrelated and depend upon the particular hydroxyfunctional epoxy resin, polycaprolactone diol, crosslinking agent,solvent and other materials, if any, and the amount of each comprisingthe coating composition. The coating compositions according to preferredembodiments of the invention, as described above, have been found toprovide the best coating results when cured at temperature at about 150°C. (300° F.) for 20 minutes. It is a highly significant advantage of theinvention, however, that these same coating compositions can withstand,for example, temperature as high as about 200° C. (390° F.) for periodsof time as long as about 60 minutes. Accordingly, great flexibility isprovided in both designing and implementing a curing schedule for partscoated with the coating compositions of the invention. Thus, in theassembly of automotive vehicles, for example, vehicles unavoidably heldin a curing oven for long periods of time during unplanned assembly lineshut-downs are recovered with cured and unharmed coatings.

High solids coating compositions according to the present invention,comprising the crosslinkable hydroxy functional epoxy resins of theinvention, especially the preferred resins described above, thepolycaprolactone diol, especially the preferred polycaprolactone dioldescribed above, and blocked polyisocyanate crosslinking agent,especially the preferred materials described above have been found toafford cured coatings with improved corrosion resistance and chipresistance, thus representing a highly advantageous advance in the art.

A most preferred use of the coating composition of the invention is as ahigh solids hot sprayable chip resistant primer for use on a bare metalsubstrate such as for an automotive vehicle body which is subject tochipping. Primer compositions typically are pigmented and any pigmentscommonly included in primer compositions for metal substrates andacrylic dispersion topcoats such as, for example, carbon black, ironoxide, lithopone, magnesium, silicate, silica, barium sulfate, TiO₂,chrome yellow, calcium chromate, strontium chromate, zinc potassiumchromate any the like may be used. The primer can be pigmented accordingto known methods including, for example, by grinding pigments in aportion of the curable resin and adding to the primer composition.

The pigment-to-binder ratio of the chip resistant primer may be fromabout 0.5:1 to about 2:1 by weight, respectively; it is preferred,however, to use a primer having a pigment-to-binder ratio of from about1:1 to about 1.5:1 by weight, respectively.

In preferred embodiments of this invention, pigments and thixotropicagents desirably are dispersed with epoxy ester resins. One type ofepoxy ester resin useful for this purpose comprises the reaction productof diepoxide, diphenol and/or dimer acid and a mixture of Soya fattyacid and propionic acid (See Example 4). Other epoxy ester resins usefulfor this purpose are those disclosed in U.S. patent application Ser.Nos. 448,886 filed June 14, 1982 (abandoned), 431,465 filed Sept. 30,1982 (abandoned) and in U.S. Pat. No. 4,491,641, all assigned to theassignee of this application. These resins comprise the simultaneousreaction product of diepoxide with (i) diphenol, dicarboxylic acid or amixture of them in chain extension reaction and (ii) fatty acid in chainterminating esterification reaction. Still other suitable epoxy resinsuseful for dispersing pigment and thixotropic agents will be apparent tothe skilled of the art in view of the present disclosure.

No special expedients are necessary in formulating the primercompositions of this invention. For example, they may be prepared simplyby incorporating the resinous components in a suitable solvent system.Thus, for example, by suitable mixing or agitation, each resinouscomponent may be dissolved in a solvent and the resulting solutionscombined to form finished primer compositions.

The solvent system may be any suitable combination of organic solventsas described above. For a high solids, hot sprayable, automotive vehiclechip resistant primer, the solvent will comprise preferably about 20 toabout 40 percent by weight of the total coating compositions, althoughof course, larger or smaller amounts may be utilized depending upon thesolids content desired.

The primer is generally maintained at about 65 to about 80 percentsolids content for hot spraying purposes with conventional thinners suchas aromatic hydrocarbons, commercial petroleum cuts which areessentially aromatic, and the like, and sprayed onto the metal base orother substrate and cured. The primer may be applied in greaterthickness of 1 to 25 mils wet, preferably 10 to 25 mils wet, in order toobtain final coatings in the desired range of 5-11 mils dry in regionshighly susceptible to chipping and is then feathered down in thicknessto the thickness of paints in areas not receiving a chip resistantprimer. The primer is cured at elevated temperatures by any convenientmeans such as baking ovens or banks of infra-red heat lamps. Curingtemperatures are preferably from about 135° C. to about 165° C.,although curing temperatures from about 100° C. to about 230° C. may beemployed, if desired.

The invention will be further understood by referring to the followingdetailed examples. It should be understood that these specific examplesare presented by way of illustration and not by way of limitation.Unless otherwise specified, all references to "parts" are intended tomean parts by weight.

EXAMPLE 1 Preparation of Hydroxy Functional Epoxy Resin

In a suitable reactor were charged 519 parts Epon 829 (trademark, ShellChemical Company, diepoxide), and 204 parts bisphenol-A. The mixture wasbrought up to 170° C. at which point an exothermic reaction occurredthat raised the temperature to 195° C. The mixture was maintained at175° C. for one hour and then cooled to 120° C. At this point, 92 partsof diethanol amine were added and a mild exothermic reaction took placewhich raised the temperature to 150° C. The batch was kept at thistemperature for one hour 815 parts of N-methyl pyrrolidone were addedand the mixture was allowed to cool. The resulting product had a Y+viscosity at 53.1% solids.

EXAMPLE 2 Preparation of Hydroxy Functional Epoxy Resin

In a suitable reactor were charged 582 parts Eponex (trademark, ShellChemical Company, diepoxide), 204 parts of bisphenol A and 0.5 parts ofsodium carbonate. The mixture was brought up to 170° C. at which pointan exothermic reaction occurred that raised the temperature to 195° C.The mixture was maintained at 175° C. for one hour and then cooled to120° C. At this point 92 parts of diethanol amine were added. Thetemperature was raised to 150° C. and kept there for one hour. 718 partsof N-methyl pyrrolidone were added and the mixture was allowed to cool.The resulting product had a viscosity of X at 55.0% solids.

EXAMPLE 3 Preparation of Hydroxy Functional Epoxy Resin

In a suitable reactor were charged 354 parts of Araldite RD-2(trademark, Ciba-Geigy Corp., diepoxide), 204 parts of bisphenol-A and0.4 parts of sodium carbonate. The mixture was brought up to 170° C. atwhich point an exothermic reaction raised the temperature to 195° C. Themixture was kept at 175° C. for one hour and then cooled to 120° C. Atthis point 92 parts of diethanol amine were added and the temperaturewas raised to 150° C. The batch was kept at this temperature for onehour. 513 parts of N-methyl pyrrolidone were added and the mixture isallowed to cool. The resulting product had a T viscosity at 55% solids.

EXAMPLE 4 Preparation of Epoxy-Ester Dispersing Resin

Into a suitable reactor were charged 1280 parts Epon 829 (trademark,Shell Chemical Company, diepoxide), 954 parts Empol 1016 (trademark,Emery Ind., Inc., dimer acid), 364 parts Soya fatty acid, 268 parts2,2-bis(hydroxymethyl) propionic acid, and 13 parts lithiumneodecanoate. The temperature of the mixture was brought up to about180° C., at which point an exothermic reaction takes place that raisedthe temperature to about 200° C. After one hour, the acid number wasfound to be less than 2. 940 parts Solvesso 100 and 305 parts Solvesso150 were added, and the mixture was cooled. The resin had a viscosity ofZ₇ at 70.0% solids.

EXAMPLE 5 Preparation of Blocked Polyisocyanate Crosslinking Agent

Into a suitable reactor were charged 870 parts methylethyl ketoxime and180 parts Solvesso 100. 1330 parts of PAPI 27 (trademark, The UpJohnChemical Co., aromatic polyisocyanate) was added dropwise to the mixtureover two hours; the reaction temperature rose from room temperature to80°-95° C. 39 parts 2-ethylhexanol was added to the mixture and thetemperature of the mixture

was maintained at 85°-95° C. for one hour. At that point, 816 parts ofM-pyrol was added and the mixture was cooled. The resulting resin wasdark brown and had a viscosity of 6000 cps at 67.0% solids.

EXAMPLE 6 Preparation of Blocked Polyisocyanate Crosslinking Agent

Into a suitable reactor were charged 537 parts methylethyl ketoxime. 784parts PAPI 94 (trademark, The UpJohn Chemical Co., aromaticpolyisocyanate) was added dropwise over two hours; the reactiontemperature rose from room temperature to 85°-95° C. The mixture wasmaintained at 85°-95° C. for one hour. The mixture was then checked toinsure compete reaction of the isocyanate by infrared spectroscopy. Atthat point, 300 parts methylamyl ketone and 150 parts M-pyrol were addedand the mixture was cooled. The resulting resin was dark brown and was75% solids.

EXAMPLES 7-10 Preparation of Blocked Polyisocyanate Crosslinking Agent

Blocked polyisocyanate crosslinkers according to the invention wereprepared in the manner of Example 6. The components employed are shownin the table below.

    ______________________________________                                                     Example                                                          Composition    7       8        9      10                                                  Parts                                                            ______________________________________                                        L-2991 A*      360     360      360                                           Desmodur IL*                           525                                    ethyl amyl ketoxime                                                                          174                      87                                    benzotriazole          238                                                    epsilon-caprolactam             228                                           N--methyl pyrrolidone                                                                        133     150      195    461                                    % solids        80       80.1     75.1  57                                    Viscosity      Z.sub.1 Z.sub.6  Z.sub.2                                                                              Z                                      ______________________________________                                    

EXAMPLE 11 Millbase Preparation

In a one gallon can or ballmill were charged the following materials andone quart of diagonal shot. The mixture was placed on a roller mill for16-24 hours to reach a 7+ hegman dispersion. At that point, the letdownwas added, and the mixture was run an additional hour on the rollermill.

    ______________________________________                                                           Parts                                                      ______________________________________                                                 Hi-Sol #3*  585                                                               2-Ethyl Hexanol                                                                            95                                                               Polyethylene Wax                                                                           70                                                               Anti-Terra-U**                                                                             40                                                               Resin of Example 4                                                                        103                                                               Barytes     2259                                                              TiO.sub.2   429                                                               Carbon Black                                                                               29                                                               Strontium Chromate                                                                        143                                                      Letdown:   Resin of Exampe 4                                                                           247                                                  ______________________________________                                         *Trademark of Ashland Chemical Co., Columbus, Ohio; HiSol #3 is an            aromatic solvent.                                                             **Trademark of Byk Mallinckrodt, Wallingford, Ct 06492; AntiTerra-U is an     antisettling and wetting agent.                                          

EXAMPLE 12 Bentone Gel Prepartion

To a clean Ball Mill were charged the following:

    ______________________________________                                                              Parts                                                   ______________________________________                                        Solvesso 150            513                                                   Propylene Carbonate     13                                                    Bentone 38              30                                                    Grind 30 minutes, then add                                                                            384                                                   Resin of Example 4                                                            Grind approximately 2 Hrs. to 8 Hegman                                        Letdown with:                                                                 Solvesso 150            60                                                                            1000                                                  ______________________________________                                    

EXAMPLES 13-15

Coating compositions of the invention were formulated as shown below.

    ______________________________________                                                        Example                                                                       13      14     15                                             Composition       Parts                                                       ______________________________________                                        Resin of Example 1                                                                              1697                                                        Resin of Example 2          1635                                              Resin of Example 3                 1635                                       Millbase of Example 11                                                                          5788      5788   5788                                       Tone 0260.sup.1   950        950    950                                       Bentone Gel of Example 12                                                                       2315      2315   2315                                       Crosslinker of Example 5                                                                        984               984                                       Crosslinker of Example 6                                                                        1050                                                        Dislon.sup.2      114        120    114                                       Cab-O-Sil.sup.3   142               142                                       ______________________________________                                         .sup.1 Trademark of Union Carbide, Danbury, Connecticut TONE 0260 is a        polycaprolactone diol.                                                        .sup.2 Trademark of Kusumoto Chemicals, Ltd.; Dislon is an antisagging        agent.                                                                        .sup.3 Trademark of Cabot Corp., Boston, Mass.; CabO-Sil is a fumed silic     (antisettling agent).                                                    

The coating compositions were prepared by sequential mixing in a 5gallon working capacity EMCO Proto-Lab SW Mill (trademark), Epworth Mfg.Co., South Haven, Mich., set at 900 rpm. Resin and Dislon (trademark)were first mixed for approximately 10 minutes and then millbase, Bentonegel and crosslinker were added sequentially while mixing. FinallyCab-O-Sil (trademark) was added and the composition mixed until a grindof 6+ on the Hegman scale was obtained.

The above compositions were sprayed at 140°-160° C. using hot-sprayequipment commercially available from Nordson Corp. Unpolished Bonderitesteel panels were sprayed and baked at 135° C. for 20 minutes. Thethickness of the coating tested varied from 5 mils to 12 mils. Thepanels were top-coated with white enamel and tested for chip resistanceusing 10 pts. of gravel in the gravelometer test. All the abovecompositions exhibited excellent chip resistance. In addition, panelswere tested for corrosion resistance (500 hrs. salt spray test, scribedpanels) and humidity resistance with excellent results.

EXAMPLES 16-19

Additional coating compositions according to the invention are shownbelow.

    ______________________________________                                                        Example                                                                       16   17        18    19                                       Composition       Parts                                                       ______________________________________                                        Resin of Example 2                                                                              1635   1635     1635 1635                                   TONE 0260.sup.1    950    950      950  950                                   Millbase of Example 11                                                                          5788   5788     5788 5788                                   Gel of Example 12 2315   2315     2315 2315                                   Crosslinker of Example 7                                                                         922                                                        Crosslinker of Example 8  922                                                 Crosslinker of Example 9           984                                        Crosslinker of Example 10              1294                                   Dislon.sup.2       100    100      100  100                                   ______________________________________                                         .sup.1 Trademark of Union Carbide, Danbury, Conn. TONE 0260 is a              polycaprolactone diol.                                                        .sup.2 Trademark of Kusumoto Chemicals, Ltd. Dislon is an antisagging         agent.                                                                   

INDUSTRIAL APPLICATION

It will be apparent from the foregoing that this invention hasindustrial applicability as a coating composition, especially as a hotsprayable, high solids coating composition suitable for use as a chipresistant automotive vehicle primer adapted for use on body panel areassubject to chipping by stones, gravel and other road debris.

In view of this disclosure, many modifications of this invention will beapparent to those skilled in the art. It is intended that all suchapparent modifications fall within the true scope of this invention andbe included within the terms of the appended claims.

What is claimed is:
 1. An organic solvent based, thermosetting coatingcomposition comprising:(A) hydroxy functional epoxy resin having anumber average molecular weight (Mn) between about 1,000 and about 4,000and being the reaction product of hydroxy functional secondary amine, inchain terminating reaction, in approximately 1 to 1 equivalent ratiowith the chain extension reaction product of diepoxide with diphenol;(B) linear polycaprolactone diol having a molecular weight of betweenabout 1500 and about 5000, wherein said (A) and (B) are included in saidcomposition in a weight ratio between about 4:1 and 1:4; and (C) blockedpolyisocyanate crosslinking agent comprising at least two isocyanategroups which have been blocked by reaction with an active hydrogenbearing blocking agent, which crosslinking agent de-blocks at the curetemperature of said composition, said crosslinking agent being includedin said composition in an amount equal to between about 10 and about 50percent of the combined weight of said (A) and (B) in said composition.2. A solvent based, thermosetting coating composition in accordance withclaim 1, wherein said polycaprolactone diol has a molecular weightbetween about 2000 and
 4000. 3. A solvent based, thermosetting coatingcomposition in accordance with claim 1, wherein said (A) and (B) areincluded in said composition in a weight ratio of about 1:1.
 4. Asolvent based, thermosetting coating composition in accordance withclaim 1, wherein said blocked polyisocyanate crosslinking agent isincluded in said composition in an amount equal to between about 20 andabout 40 percent of the combined weight of components (A) and (B) insaid composition.
 5. A solvent based, thermosetting coating compositionin accordance with claim 1, wherein said diepoxide is selected from thegroup consisting of bisphenol-A epichlorohydrin epoxy resin, hydantoinepoxy resin, cyclic and acyclic aliphatic diepoxides and mixturesthereof.
 6. A solvent based, thermosetting coating composition inaccordance with claim 1, wherein said diphenol is selected from thegroup consisting of bisphenol-A, bisphenol-B, bisphenol-F and mixturesthereof.
 7. A solvent based, thermosetting coating composition inaccordance with claim 1, wherein said hydroxy functional secondary amineis selected from the group having the general formula: ##STR11## whereinR and R' are selected from aliphatic, cycloaliphatic and aromaticradicals which will not interfere with the chain termination reaction ofsaid diepoxide and said hydroxy functional secondary amine to form saidhydroxy functional epoxy resin, and wherein X is selected from the groupconsisting of hydrogen and hydroxyl radical.
 8. A solvent based,thermosetting coating composition in accordance with claim 7, whereinsaid hydroxy functional secondary amine bears primary hydroxylfunctionality.
 9. A solvent based, thermosetting coating composition inaccordance with claim 8, wherein said hydroxy functional secondary amineis selected from the group consisting of diethanol amine, methylethanolamine, dipropanol amine and methylpropanol amine.
 10. A solvent based,thermosetting coating composition in accordance with claim 1, whereinsaid linear polycaprolactone diol is the product of polymerization oflactone monomers in the presence of initiator compounds having twofunctional groups each having an active hydrogen capable of opening thelactone and at a temperature between about 50° C. and about 300° C.,said lactone monomers having the general formula: ##STR12## wherein n isat least 4, at least n+2 R's are H and the remaining R's aresubstitutents selected from the group consisting of alkyl, cycloalkyl,alkoxy and single ring aromatic hydrocarbon radicals.
 11. A solventbased, thermosetting coating composition in accordance with claim 10,wherein said initiator compounds are selected from the group consistingof diamines, diols, amino alcohols, diacids and hydroxy carboxylicacids.
 12. A solvent based, thermosetting coating composition inaccordance with claim 10, wherein said lactone monomers areepsilon-caprolactone monomers having the general formula: ##STR13##wherein at least 6 of the R's are hydrogen and the remainder areselected from the group consisting of alkyl, cycloalkyl, alkoxy andsingle ring aromatic hydrocarbon radicals, wherein none of thesubstitutents contain more than about 12 carbon atoms and wherein thetotal number of carbon atoms in the substitutents on a lactone ring doesnot exceed about
 12. 13. A solvent based, thermosetting coatingcomposition in accordance with claim 12, wherein said lactone monomerscomprise unsubstituted epsilon-caprolactone monomers.
 14. A solventbased, thermosetting coating composition in accordance with claim 1,wherein:(a) said polycaprolactone diol is the product of polymerizationof lactone monomers in the presence of initiator compounds having twofunctional groups each having an active hydrogen capable of opening thelactone ring at a temperature of between about 50° C. and 300° C., saidlactone monomers having the general formula: ##STR14## wherein n is atleast 4, at least n+2 R's are hydrogen, and the remaining R's aresubstitutents selected from the group consisting of alkyl, cycloalkyl,alkoxy and single ring aromatic hydrocarbon radicals; and (b) the chainextended diepoxide is the reaction product of said diepoxide selectedfrom the group consisting of bisphenol-A epichlorohydrin epoxy resin,hydantoin epoxy resin, cyclic and acyclic aliphatic diepoxide, and amixture of any of them with said diphenol selected from the groupconsisting of those having the general formula: ##STR15## wherein R is adivalent, organic linking moiety substantially unreactive with the epoxyfunctionality of said diepoxide; and (c) said hydroxy functionalsecondary amine is selected from the group having the general formula:##STR16## wherein R and R' are selected from the group consisting ofaliphatic, cycloaliphatic and aromatic radicals which will not interferewith the chain termination reaction of epoxide and the hydroxyfunctional secondary amine, X is selected from the group consisting ofhydrogen and hydroxyl group, and at least a portion of hydroxyl groupson said hydroxy functional secondary amine are primary.
 15. A solventbased, thermosetting coating composition in accordance with claim 1,wherein said blocked polyisocyanate is selected from blocked aliphatic,aromatic, cycloalkylene, aliphatic aromatic and nuclear substitutedaromatic polyisocyanates.
 16. A solvent based, thermosetting coatingcomposition in accordance with claim 1, wherein said blockedpolyisocyanate crosslinking agent comprises blocked polymethylenepolyphenol isocyanate which unblocked has the formula: ##STR17## whereinn equals 1 to
 3. 17. A solvent based, thermosetting coating compositionin accordance with claim 1, wherein the polyisocyanate employed in thepreparation of said blocked polyisocyanate crosslinking agent comprisesisocyanurate ring containing polyisocyanate prepared bycyclotrimerization of diisocyanate.
 18. A solvent based, thermosettingcoating composition in accordance with claim 1, wherein said blockedpolyisocyanate crosslinking agent is the reaction product of:(a) thereaction product of (i) organic diisocyanate represented by the formula:

    OCN--R--NCO

wherein R is selected from the group consisting of aliphatic,cycloaliphatic and aromatic radicals and combinations thereof andwherein one of the isocyanate groups thereof is a more reactiveisocyanate group than the other isocyanate group and (ii) sufficientactive hydrogen containing blocking agent to react with substantiallyall of said more reactive isocyanate groups; and (b) sufficient polyolto react with substantially all of said other isocyanate groups.
 19. Asolvent based, thermosetting coating composition in accordance withclaim 1, adapted to be used as a chip resistant primer to be sprayed atelevated temperature, wherein the solids level of the composition is inthe range of 60-80% by weight.
 20. A organic solvent based,thermosetting coating composition comprising:(A) hydroxy functionalepoxy resin having a number average molecular weight (Mn) between about1,000 and about 4,000 and being the reaction product of hydroxyfunctional secondary amine bearing primary hydroxyl groups, in chainterminating reaction, in approximately 1 to 1 equivalent ratio with thechain extension reaction product of diepoxide selected from the groupconsisting of bisphenol-A epichlorohydrin epoxy resin, hydantoin epoxyresin, cyclic and acyclic aliphatic diepoxide, and a mixture of any ofthem, with diphenol selected from the group consisting of bisphenol-A,bisphenol-B, bisphenol-F and mixtures thereof; (B) linearpolycaprolactone diol having a molecular weight of between about 1,500and about 5,000 made by polymerizing epsilon-caprolactone monomers inthe presence of initiator compounds having two functional groups eachhaving an active hydrogen capable of opening the lactone ring at atemperature of between about 50° C. and about 300° C., wherein said (A)and (B) are included in said composition in a weight ratio between about4:1 and 1:4; and (C) blocked polyisocyanate crosslinking agentcomprising at least two isocyanate groups which have been blocked byreaction with an active hydrogen bearing blocked agent, whichcrosslinking agent de-blocks at the cure temperature of said coatingcomposition, said blocked polyisocyanate being selected from blockedaliphatic, aromatic, cycloalkylene, aliphatic aromatic, and nuclearsubstituted aromatic polyisocyanates and being included in saidcomposition in an amount equal to between about 10 and about 50 percentof the combined weight of said (A) and (B) in said composition.